Răspuns :
a+b+c=70
a/3=b/4=c/7
a=3k
b=4k
c=7k
3k+4k+7k=70
14k=70
k=70:14
k=5
a=3×5
a=15
b=4×5
b=20
c=7×5
c=35
[tex]\it \dfrac{a}{3}= \dfrac{b}{4}= \dfrac{c}{7} = \dfrac{a+b+c}{3+4+7}= \dfrac{70}{14}=5\Rightarrow\begin{cases}\it a=3\cdot5=15\\ \\ \it b=4\cdot5=20\\ \\ \it c=7\cdot5=35\end{cases}[/tex]